Power operated rotary knives have been in wide-spread use in meat packing and other commercial food processing facilities. These knives usually comprised a handle and a blade housing that supported an annular knife blade. The knife blade was driven about its central axis relative to the blade housing by a motor via a gear train.
The knife blade comprised an annular body, a blade section projecting axially from the body and driving gear teeth projecting axially from the body oppositely from the blade section. The blade housing maintained the blade in position relative to the knife as the blade rotated. The blade was subjected to various forces created by both the drive transmission and the cutting action of the knife.
In some knives the blade housing defined a blade supporting race in the form of a peripheral groove that was rectilinear in cross sectional shape for receiving the blade body and gear teeth. These blade housings were frequently split and were resiliently expandable to receive the blade. The blade body and gear teeth were shaped to confront the axially opposite blade race sides with running clearance just sufficient to prevent the blade from binding in the groove. Consequently the blade and blade housing were slidably engaged over relatively wide contact areas.
In some other knives the blade housings had a radially inwardly extending lip that defined a frustoconical surface engaging a frustoconical blade surface to prevent the blade from separating axially from the blade housing. In such cases, the knives also comprised a shoe that pivoted into engagement with the blade. The shoes also provided frustoconical surfaces that wedged the blade toward the blade housing and retained the blade in place.
Some prior art rotary knives tended to vibrate undesirably in use because the blade rotation axis was permitted to shift relative to the blade housing. Put another way, the blade tended to bounce around within the blade housing so that the entire knife vibrated. In the knives where the blade was secured to the knife by confronting wedging surfaces, the blade vibration caused the blade to shift axially into undesired contact with the blade housing. This axial blade movement contributed both to knife vibration and blade heating. In order to constrain the blade to rotate about an axis that was relatively fixed with respect to the blade housing, the blade housing diameter was adjusted to minimize the radial clearance between the radially outer blade body and gear surfaces and the radially outer race surface. This reduced vibration.
Although vibration was reduced, other problems were created. First, where the blade housing was adjusted to provide a tight running clearance, heat generated by frictional contact between the blade and blade support was often sufficient to begin to cook the product being trimmed. The heated product created a sticky build-up on the knife parts that generated even more friction heat. In some circumstances, when the housing diameter was adjusted, the race became slightly out of round, or out of plane. This condition tended to contribute to both vibration and overheating.
The usual approach to ameliorating these problems was to assemble the blade and housing with running clearances that were tight enough to keep vibration at tolerable levels yet open enough to avoid overheating. Another practice used to reduce vibration and heating was to operate the knife at relatively low rotational speeds. User effort required to operate the knife increased with lowered operating speeds because the slicing action was reduced. Despite these efforts, the prior art knives tended to both vibrate and run hot. Where operated at low speeds, the vibration and friction heating were accompanied by increased user effort.
The present invention provides a new and improved annular blade for a rotary knife wherein the blade is supported for rotation about a central axis at a plurality of line contact bearing locations, resulting in a knife that exhibits minimal vibration and heating and may be operated at relatively high speeds so that user effort is reduced.